The invention relates to a system for transmitting and receiving a television signal via a transmission channel, comprising at least a transmitting section and a receiving section, the transmitting section including a sampling circuit for sampling each field of the television signal in accordance with a sampling pattern which is shifted field-sequentially at least in the horizontal direction.
A system of this type is known from NHK Laboratories Note, Ser. No. 304, September 1984. In the transmitting section of the system described in this Article the television signal from a source having 1125 lines per picture distributed in an interlaced manner over 2 fields at a field frequency of 60 Hz, is sampled in accordance with 4 different sampling patterns shifted field-sequentially at least in the horizontal direction. In the receiving section a signal which is obtained by spatial interpolation within one received field is mixed, dependent on a measured amount of movement in the television signal, with a signal obtained from a collection of each time four successively received fields. In the case of still pictures or pictures exhibiting little movement the mixing result will be predominantly determined by the signal obtained from this collection. Since all sampling values of four successive fields can be used, a display with a maximum spatial resolution can be achieved which is, however, at the expense of a temporal resolution which is of no importance in the case of still pictures and of lesser importance in pictures exhibiting little movement. In this connection the temporal resolution is understood to mean a number of movement phases per unit of time. On the other hand, in the case of fast movements, the mixing result will be predominantly determined by the signal obtained by spatial interpolation, thus avoiding motion blur as much as possible. Since in this case the sampling values of only one field are used, the spatial resolution is less than in the case of still pictures. Use is made of the fact that a viewer is less sensitive to shortcomings in the spatial resolution in the picture in the case of fast movements, so that there arises room for a larger temporal resolution with a simultaneous decrease of the spatial resolution. It will be evident that in view of the limited bandwidth of the transmission channel it is not possible to transmit a television signal suitable for a display with a large temporal and simultaneously a large spatial resolution. Dependent on the amount of movement in the pictures to be displayed by means of the television signal it is possible to transmit a television signal suitable for the display with the combination of special and temporal resolution which is most favourable to the viewer. The maximum temporal resolution is, however, limited by the field frequency of 60 Hz. This drawback occurs to a greater extent if such a system must be suitable for a transmission channel for 625 lines per picture, distributed in an interlaced manner over 2 fields at a field frequency of 50 Hz as is used, for example, for the known European MAC system and if it must also be compatible therewith. This compatibility implies that also MAC receivers without special facilities should be capable of processing a television signal transmitted by the transmitting section of the system.